The present invention, in some embodiments thereof, relates to stents and stent jacket assemblies and, more specifically but not exclusively, to low bulk stent jackets designed to resist damage during stent expansion while providing protection against embolitic debris release into the general circulation.
The use of stents to prevent restenosis in treated stenotic vasculature began in 1994 following U.S. Food and Drug Administration approval of the Palmaz-Schatz stent.
Stents made of elastic and/or plastic materials are typically expanded by inflating a balloon within the contracted stent. After stent expansion, the balloon is deflated and removed from the vasculature, leaving the stent in place. Stents containing superelastic materials, for example nitinol, are passed through the vasculature enclosed within a sheath that is retracted to allow stent release and simultaneous expansion.
While stents have resulted in improved long-term blood flow, stents are associated with severe problems during and immediately following stent placement. Stents generate debris from stenotic tissue that enter the general circulation and travel to vital organs, for example the brain and/or lungs, causing vascular blockage, tissue necrosis and/or patient death. Debris generation is endemic to all stents including stents used in chronic heart conditions, carotid arteries, degenerated saphenous vein grafts, and in thrombotic lesions associated with acute coronary syndromes.
The association between stents and life-threatening debris is related to both the vascular environment and stent architecture. The stenotic vessel where the stent is deployed is generally lined with relatively brittle plaques. A conventional stent is typically constructed from a relatively stiff material having large mesh-like apertures that scrape against the surrounding vessel as the stent contracts longitudinally during expansion.
Plaque portions that protrude through the stent apertures are subjected to shear forces and rip loose, creating debris that pass through the stent lumen and into the general circulation.
To reduce the amount of debris entering the circulation, stents are often deployed in conjunction with stent jackets made of a material having small apertures. Stent jackets are typically formed by a process including, inter alia interlocked knitting, braiding, interlacing, and/or dipping a porous mold into one or more reagents.
Jacketed stents in general pose a problem in that the coefficient of expansion of the jacket is typically different from the coefficient of expansion of the associated stent. A jacket located on the outside of the stent, where the jacket provides the greatest protection against debris, must be secured to the stent to maintain proper alignment during stent deployment. The difficulty of securing a jacket with a first coefficient of expansion to a stent having a second coefficient of expansion substantially prevents locating a jacket external to the stent.